Re: [linuxsh-dev] Cache bug on SH-3/4

[Stuart M. <stu...@st...>]

Hi Paul

This looks like a problem I hit a short while ago when using ssh. Turns
out to be a problem in the generic kernel code, which is using a
clear_highpage() to zero the page, which doesn't have the necessary extra
cache alias prevention code. Ideally it should be replaced by
clear_user_page(), but the virtual address where the page is going to be
mapped isn't available at that point in the code.

At this point I had a look in Marcello's tree in BK, and it turns out
somebody else has already fixed this problem by simply adding a call to
flush_dcache_page(). IIRC this is a post 2.4.20 change.

I'm running with the attached patch to a 2.4.18 tree, and your test
code appears to work for me on an SH4, I've not tried anything else.

Hope this helps

Stuart

On Fri, 14 Feb 2003 08:47:07 -0500 pau...@ti... wrote:

> I've hit what looks to be another cache bug (looks like its an alias
> issue), and so far it seems to hit both SH-3 and 4. (I haven't tested
> SH-2 or 5 yet).
> 
> The problem pops up when doing an mmap() of /dev/zero and then reading
> from it, the read is sometimes 0, but most of the time ends up getting
> back garbage and promptly segfaulting.
> 
> I've attached my testcode for this as well. The fault happens right on
> the read.
> 
> I've managed to fix this on SH-4 (patch attached) by doing an all out
> flush_cache_all() after the activate_context() in switch_mm() .. not a
> very optimal solution, but seems to do the right thing for now.
> 
> Unfortunately this same fix doesn't help SH-3 any (after implicitly
> wrapping flush_cache_all() to cache_wback_all()).
> 
> Anyone seen this before?
> 
> Regards,
> 
> -- 
> Paul Mundt <pau...@ti...>
> TimeSys Corporation
>